Various concentration measuring apparatuses have previously been developed which place a transmitter and a receiver in a substance to be measured, transmit sound waves or light waves from the transmitter in the direction of the matter suspended in the liquid constituting the object of measurement, and measure the amount of attenuation or amount of scattering thereof at the receiver, to thereby measure the concentration of suspended matter in the substance which is to be measured.
In the conventional apparatuses described above, the transmitting surface of the transmitter and the receiving surface of the receiver are in direct contact with the liquid which is the substance to be measured, so that a material such as suspended matter present in the substance which is to be measured, or matter which is dissolved in the substance to measured or is present as impurities therein is deposited or generated thereon, and thereby, the transmitting surface of the transmitter and the receiving surface of the receiver are contaminated.
The contamination as a result of deposition or generation on the transmitting surface or the receiving surface as described above alters the amount of transmission, amount of attenuation, amount of scattering, and the like of the sound waves or light waves, and causes errors in the measured values, so that it becomes impossible to make accurate concentration measurements. Thus, particularly, in concentration measurement apparatuses which are used under conditions of severe contamination, it is necessary to remove the contaminants deposited on the transmitting surface and the receiving surface. Conventionally, methods for the removal of contaminants deposited or generated thereon have included methods which mechanically remove deposited matter, such as manual cleaning, washing with water, or washing in the presence of ultrasonic waves.
Removal methods for deposited matter which were conventionally conducted adopted, with the exception of the case in which manual cleaning was conducted, a mechanism in which washing was automatically conducted. However, the use of such automatic washing mechanisms is not necessarily sufficient, and in particular, in applications having as the object thereof substances to be measured in which contaminants are easily deposited, such as sewage sludge and the like, the reliability of the values measured by means of a concentration meter employing the amount of attenuation or the amount of scattering in sound waves or light waves must of necessity be rather low. Furthermore, in a manual cleaning, as the pace of contamination, is faster, the troublesome of the cleaning can not be avoided, and there is a problem in that continuous measurement cannot be attained.
The present invention has as an object thereof to provide a concentration measurement apparatus which is capable, even in applications in which contaminants are easily deposited, such as when sewage sludge is the object of the measurement as described above, of accurately measuring the concentration of suspended matter present in a substance to be measured by means of providing a method by which contamination is not deposited or generated on the transmitting surface of the transmitter or on the receiving surface of the receiver, and by transmitting a stipulated amount of sound waves or light waves in the direction of matter suspended in a liquid which is to be measured, and receiving the amount of attenuation or amount of scattering thereof in a manner unaffected by the contamination.